Cancers and tumors can be controlled or eradicated by the immune system. The immune system includes several types of lymphoid and myeloid cells, e.g., monocytes, macrophages, dendritic cells (DCs), eosinophils, T cells, B cells, and neutrophils. These lymphoid and myeloid cells produce secreted signaling proteins known as cytokines. The cytokines include, e.g., interleukin-10 (IL-10), interferon-gamma (IFNγ), IL-12, and IL-23. Immune response includes inflammation, i.e., the accumulation of immune cells systemically or in a particular location of the body. In response to an infective agent or foreign substance, immune cells secrete cytokines which, in turn, modulate immune cell proliferation, development, differentiation, or migration. Excessive immune response can produce pathological consequences, such as autoimmune disorders, whereas impaired immune response may result in cancer. Anti-tumor response by the immune system includes innate immunity, e.g., as mediated by macrophages, NK cells, and neutrophils, and adaptive immunity, e.g., as mediated by antigen presenting cells (APCs), T cells, and B cells (see, e.g., Abbas, et al. (eds.) (2000) Cellular and Molecular Immunology, W.B. Saunders Co., Philadelphia, Pa.; Oppenheim and Feldmann (eds.) (2001) Cytokine Reference, Academic Press, San Diego, Calif.; von Andrian and Mackay (2000) New Engl. J. Med. 343:1020-1034; Davidson and Diamond (2001) New Engl. J. Med. 345:340-350).
Methods of modulating immune response have been used in the treatment of cancers, e.g., melanoma. These methods include treatment either with cytokines such as IL-2, IL-10, IL-12, tumor necrosis factor-alpha (TNFalpha), IFNγ, granulocyte macrophage-colony stimulating factor (GM-CSF), and transforming growth factor (TGF), or with cytokine antagonists (e.g., antibodies). Interleukin-10 was first characterized as a cytokine synthesis inhibitory factor (CSIF; see, e.g., Fiorentino, et al (1989) J. Exp. Med. 170:2081-2095). IL-10 is a pleiotropic cytokine produced by T cells, B cells, monocytes, that can function as both an immunosuppressant and immunostimulant (see, e.g., Groux, et al. (1998) J. Immunol. 160:3188-3193; and Hagenbaugh, et al. (1997) J. Exp. Med. 185:2101-2110).
Animal models suggest that IL-10 can induce NK-cell activation and facilitate target-cell destruction in a dose-dependent manner (see, e.g., Zheng, et al. (1996) J. Exp. Med. 184:579-584; Kundu, et al. (1996) J. Natl. Cancer Inst. 88:536-541). Further studies indicate that the presence of IL-10 in the tumor microenvironment correlates with better patient survival (see, e.g., Lu, et al. (2004) J. Clin. Oncol. 22:4575-4583).
Unfortunately, the serum half life for IL-10 is relatively short, i.e., 2-6 hours (see, e.g., Smith et al. (1996) Cellular Immunol. 173:207-214). The present invention addresses this problem by providing methods of using an engineered form of IL-10, e.g., a pegylated IL-10, to treat cancer. In addition to a longer serum half life, the pegylated form of IL-10 surprisingly exhibited increased tumor killing activity, for example, through increased recruitment of CD8+ T cells to the tumor site, when compared to non-pegylated IL-10.